Antenna control

ABSTRACT

An automatic control for a motorized directional antenna of the type used for reception of a high frequency broadcast signals. The control includes electronic circuitry for monitoring the incoming signal input at a broadcast receiver and electronically comparing the received signal to a signal of maximum strength from the signal source received during movement of the antenna, together with a logic-controlled switching circuit that causes the antenna motor to reverse in a predetermined pattern to hunt and aim the antenna at an angular position at which the maximum signal strength is received.

I United States Patent [1 1 [111 3,798,649

Houng Mar. 19, 1974 ANTENNA CONTROL Primary Examiner-Maynard R. Wilbur[76] Inventor: Shunien Houng, 917 E. DeSmet, Assistant Examiner-TheodoreBlum Spokane Wash 99202 Attorney, Agent, or Ftrm-Wells, St. John &Roberts [21] Appl. No.: 283,951 An automatic control for a motorizeddirectional antenna of the type used for reception of a high fre- [52]CL 343/117 R quency broadcast signals. The control includes elec- [51]Int Cl G015 1/44 tronic circuitry for monitoring the incoming signal[58] Field 343/117 R input at a broadcast receiver and electronicallycoma "5 7 'paring the received signal to a'signal of maximum [56]References Cited strength from the signal source received duringmovement of the antenna, together with a logic-controlled UNITED STATESPATENTS switching circuit that causes the antenna motor to re- 333719696/1973 343/117 R verse in a predetermined pattern to hunt and aim theatoms g antenna at an angular position at which the maximum ogers....3,686,671 8/1972 Holley 343/117 R slgnal Strength recewed' MECHAMlCN.COUPLJMG 4 Claims, 11 Drawing Figures I votmcrr. i coMPARAron Vt RESETno.2. l i l l {g l 2 i 1 MAXIMUM vomaea R E SGNAL com R Ei BNARY AMTEWXAAMPLIFIER 'm' DETECTOR NOAIA COUNTER /0 ('5 (7x 1 i MEMORY SWITCHWGERASER C\RCUIT I w MOTOR J (DUTROL PAIENTEDIIIAR I 9 I974 3Q798649 SHEET1 {IF 3 MECHAMICN. COUPLING VOLTAGE. I QOMRARATOR VT RESET I No.2. I 5 6I4 I M I x ANTENNA R E I IGwA L a LCfiki??? E; r BINARY AMPLIFIER vm'DETECTOR 4 COUNTER /0 g,

(5 FIGI (2x I! I MEMORY SWITCHING ERASER C\RCUIT FIG 2 30 X I fl/FZ/TIZI 38 J( MOTOR I M x OUTPUT V: 20 4 In 'ZfififQQ-p 5r COLITROL TK'KMVVI) 27 32 Z4 26 M 26 L22 25 r I. G I I I I I o I l I I AA/rew v V0O/TFZ/T I I I AA/GZE FIG 3 Q I I I 79 l/ o I I I I I #955 010 I I IIAA/TEA/NA VOLTAGE. I I I ANGLE COMPARATOR I I I I I 4 q /g/ OUTPUTVOLTAGE H H LOG/CO 0 ANTENNA ANGLE PATENTEUMAR 1 9 1914 3; 798 649 SHEET3 OF 3 AUIZA/A/A FIG 7 g a Q R J I 0. Ac. 44 w MOTOR ga a g2 43 A- F T LFIG 8 VAR/A BLES F LIA/C 7704/5 Q. Q 6 M F R I I 0 O I I I O O O I O I IO I I 0 I O I I O I 0 I 0 1' 0 r I 0 I I 0 I O O O O O O I I 0 I I O I OI I O I I O O I O O I I I O ANTENNA CONTROL BACKGROUND OF THE INVENTIONThis disclosure relates to an electronic circuit for au tomaticallycontrolling rotation of a directional broadcast receiving antenna toobtain maximum signal strength. The circuitry operates independent ofany external or manual controls to automatically turn the antenna tohunt the rotational position at which maximum signal strength isachieved. To assure that the rotatable antenna is positioned properly,the control circuitry for the antenna motor is programmed logically tomove the antennaangularly beyond the desired posi: tion and reverse itsrotation in repetitive pattern of angular movement to return suchlocation once it has been located.

Many prior efforts have apparently been directed to mechanization ofantenna control. The most common system is a simple manual controlswitch that allows a person to manually operate the rotor for theantenna and set it at a desired angular position when changing stationsat the broadcast receiver. An example of such a system is shown in theJordan U. 5. Pat. No. 2,498,957.

The prior U. S. Pat. No. 2,597,424 to Znaidukas, shows an automaticcontrol system, but it seeks a signal of predetermined strength. It isnot designed to seek maximum strength regardless of the specificamplitude of the signal.

The Bennett U.S. Pat. No. 3,197,683 discloses a pulse-controlled systemfor an antenna rotor, but this requires presetting of the antenna foreach input pulse signal. Each installation must be properly preset andsuch a device would not automatically seek new sta tions or signalscoming from a broadcast antenna that has been physically relocated. Thepatents to Blauvelt, U. S. Pat. Nos. 2,872,631 and Lunn, 3,043,998represent other prior attempts to provide semi-automatic control of atelevision antenna. However, these arrangements also require eithermanual setting of a control or presetting to match station location atthe time of installation.

SUMMARY OF THE INVENTION This invention provides an electronic controlfor a reversible motor having a rotatable shaft that angularly turns adirectional antenna for high frequency broadcast signals, such as atelevision or FM broadcast receiving antenna. A memory circuit monitorsthe strength of the instantaneous signal received by the receiver andstores the maximum signal received during each operating sequence. Thesignals are compared by a comparator circuit which produces a digitaloutput signal when the comparative signal reaches a predetermined level.A binary counter receives the digital signal and produces alternatecontrol signals in response to its detection ofa sequence of reversal inthe digital output signal pattern. Eletronic switch circuits areoperatively connected to the binary counter and to a motor controlcircuit connected to the reversible motor at the antenna to operate themotor in a preset logical sequence whereby the antenna is automaticallymoved beyond the angular position at which the maximum signal isreceived and is subsequently returned to that position and locked. Thecircuitry is then automatically reset at the conclusion of eachoperating sequence so as to be operable in a new sequence when thereceiver is subsequently tuned to another signal source.

It is a first object of this invention to provide a truly automaticsignal-sensing and seeking control for a rotatable broadcast signalreceiving antenna, operating entirely without manual intervention or anyrequirement that it be individually preset to a given location andreceiver.

Another object of this invention is to provide an automatic controlcircuit of this type which will seek out maximum incoming signals ofvarious strength.

Another object of the invention is to provide a completely electroniccontrol circuit so as to minimize mechanical problems and optimizedependability.

These and further objects will be evident from the following disclosure,which illustrates an example of a specific arrangement incorporating theinvention, It is to be understood that the specific details disclosedare presented only by way of example and that the invention itself isset out in the claims that follow the description.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified block diagram of thecontrol circuitry;

FIG. 2 is a schematic drawing of the maximum signal detector circuit;

FIG. 3 is an interrelated plot of voltages;

FIG. 4 is a simplified block diagram of the binary counter;

FIG. Sis a simplified diagram of the switching circuit;

FIG. 6 is a simplified diagram of the memory eraser circuit;

FIG. 7 is a circuit diagram of the motor control;

FIG. 8 is a logic truth table motor control;

FIG. 9 is a plot of the received signal intensity;

FIG. 10 is an interrelated plot of the received signal and controlsignals during operation of the circuitry; and

FIG. 11 is a plot similar to FIG. 10, illustrating an alternate sequenceof operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT The general arrangement of thepresent apparatus is illustrated in FIG. 1, where a conventionalrotatable high frequency broadcast receiving antenna (television, shortwave or FM) is illustrated by the block 10. The structure of suchantennas, which typically include a rotatable mast and an electricallypowered drive unit, is well-known in the art and no further descriptionis believed necessary to an understanding of the following disclosure ofcontrol circuitry for the power unit that angularly locates the antennafor maximum signal strength.

The broadcast signal received by antenna 10 is directed to aconventional amplifier 11. The amplified signal (V,,,) is directed to amaximum signal detector circuit 12, which serves as a monitor todetermine the relative intensity of the received signal during rotationof antenna 10 and as a memory to store the maximum received signal(V,,.,). The resulting differential signal voltage (V serves as acomparison of signal strengtli during an operational sequence. Thisdifferential voltage is then directed to a first voltage comparator,which converts the analog signal to a binary signal (E The binary signalis counted by a binary counter 14 that controls operation of a switchingcircuit 15. The switching circuit 15 is logically arranged or pre-set tooperate motor control 18 for antenna in a preselected reversing patternof rotation such that antenna 10 is moved beyond the angular position atwhich its maximum broadcast signal intensity is received, is thenreversed to verify the location of maximum signal intensity by againpassing the position of maximum signal intensity, and once more reversedto lock at that position. After each sequence, a memory eraser circuit17 and second voltage comparator 16 re-set the circuitry and hold theantenna at its desired position until there is change in the signalreceived at antenna 10.

It is to be noted that the above apparatus requires no manual operation.It operates automatically when the signal received at antenna 10 isvaried, which occurs normally when the receiving set is tuned to adifferent intensity or channel. In the case of a television receiver,each time that the user changes the channel being received at his set,the signal at antenna 10 will vary in frequency because the antenna willnot then be aimed at the signal source. The antenna 10 will then beautomatically rotated to seek out and lock at the angular position atwhich the received signal has its greatest in tensity. Unlike priordevices for such angular positioning, the present apparatus requires nopre-setting or calibration. It will automatically seek out each station,and does not require adjustment for new or relocated broadcast signalsources.

The details of the operating circuitry are shown schematically in thedrawings, since the basic circuits used in this combination arewell-known in electronic control and logic circuit design.

The maximum signal detector circuit 12 is illustrated in greater detailin FIG 2. It receives the amplified signal from antenna 10 and amplifier11 at input 20. This is stored in a capacitor 21 across input 20.Capacitor 21 acts as a memory device, storing the maximum input voltagefor an indefinite time during each operating sequence. It acts as astorage memory because of the very high resistance in its discharge pathwhich consists of the high input resistance of a differential amplifier22 and the high resistance of a reversed-bias diode 23.

A second capacitor 24 is also connected across input 20, along with adiode 25 and potentiometer 26. The output voltage from this secondarycircuit is directed to differential amplifier 22 at inputs 27, 28. Theinstantaneous signal directed to the differential amplifier 22 isidentified as V,-v The amplifier 22 compares this signal V, with themaximum signal stored across capacitor 21 and directed to the amplifierinput 27, 30. The output terminals 31, 32 of amplifier 22 produce adifferential signal V,, directly proportional to the difference in theinput signals. When output signal V is 0 the two input signals toamplifier 22 are equal. The relation between the angular position of theantennas, the input voltage V, and the amplifier output voltage V, isillustrated graphically in the upper two portions of FIG. 3.

The signal V is directed to a first voltage comparator 13 which convertsthe analog input signal to a digital output signal. The circuit 13responds to an arbitrary threshold voltage level, producing alternatinglogical 0 and logical 1 signals when the differential output V passesthe threshold level. The binary signal E changes from a logical l to alogical 0 when the signal V, exceeds the threshold level and returns toa logical 1 when the signal next falls below the threshold level. Theoperational sequence is illustrated at the lower portion of FIG. 3relative to the signals at circuit 12.

The binary signal is monitored by a counter diagramatically illustratedin FIG. 4. It consists of two flipflop circuits 33 connected in adivided-by-four counter configuration. The output flip-flop states areindicated by Q and 6, where 6 represents not Q, as shown in the truthtable (FIG. 8). The output from the binary counter 14 controls switchingcircuits 15.

The switching circuits, illustrated in FIG. 5, consist of three ANDgates 34, one NAND 35, and an inverter 36. The AND gates 34 provide alogical 1 output when all inputs are simultaneously present and abovethe logical 1 level. The inverter 36 inverts the input logic statement.The NAND gate is a combination of an AND gate and an inverter outputstage.

The logic statement M, R and F in the truth table, FIG. 8, represent thefunctions of the antenna rotor. M represents motor operation and F and Rrespectively represent forward or reverse movement. When M and R are 1the motor 18 rotates in reversed direction. When M and F are 1 motor 18rotates in a forward direction. When M is 0, the motor is turned off.The logic statements are expressed by the following equations? E- QT R MI (where Y= Q Q F M- 1 (where 1 Q Q The resetting of the apparatus isaccomplished in response to the input signal voltage, V as well as themotor logic statement M. A voltage comparator 16, basically identical tothe previously-described circuit 13, produces a re-set signal V, used asa re-set signal for binary counter 14 (FIG. 4) and as a trigger signalto the memory eraser circuit 17. The circuit 17 (FIG. 6) consists of anOR gate which produces a logical 1 output when either M or V, input, orboth are equal to a logical 1. The logic statement is expressed by theequation E, A V,

where 17 and V, represent, respectively, the logic statements of themotor and the reference voltage output of the voltage comparator 16.

When the motor stops, both I71 and E, are at logical 1. The memoryeraser discharges the capacitor 21 by operation of relay 38 to close thenormally-open switch 40 connected across capacitor 21. Switch 40 can beclosed manually or by operation of relay 38. This erases the storedmemory of the maximum signal and latches the antenna 10 at the maximumreceiving position because of the output of the differential amplifier22 becomes negative. Whenever the input signal V is below a referencevoltage shown arbitrarily at line 41 in FIG. 9, both E, and V, are atlogical 1. E, then erases the stored memory at capacitor 21 and V,re-sets the binary counter such that antenna 10 begins to rotate insearching for the maximum signal input the V The motor control circuit18 is basically shown in FIG. 7. The DC motor 42 is mechanically coupledto antenna 10. Its direction of rotation is controlled by twosilcon-controlled rectifiers (SCR) 43, 44 which in turn are controlledby the logical statements R and F. The power source to motor 42 is an ACpower line having terminals indicated at 45.

A typical antenna pattern during rotation of antenna is illustrated inFIG. 9. This assumes rotation in such manner as to encounter an initialincrease in signal strength. The object of the present apparatus is toset antenna 10 at the center angular position at which the intensity ofthe received signal is at a maximum, shown in FIG. 9 by the letter C.When one selects a TV station, or if the receiving signal intensityshould fall below the reference value indicated by line 411, V, is atlogical 1. This re-sets the binary counter 14 and erases the storedmemory at capacitor 21 in the maximum signal detector circuit 12.Antenna It) then begins to rotate and eventually the received signalintensity will rise above the reference level at 41, illustrated inFIGS. 9 and 10 by the letter A.

When the receiving signal V reaches A, as shown in FIG. 9, V, changes tological 0. This restores the memory at capacitor 21 and releases thereset to binary 14. These logical statements are represented by thefirst row of the truth table in FIG. 8.

When the signal V reaches the apex C, capacitor 21 will store themaximum signal voltage received. Antenna 10 will continue rotating andpass the apex C. When this decline in received signal strength issensed, at D, the outout signal E, of voltage comparator 13 will beswitched to logical 0, which will be counted by the binary counter 14and fed to the switching circuit 15. This changes the logical statementsto the second row of the truth table.

Antenna It) is then reversed in direction and goes back to the apex C,again changing the digital output of voltage comparator l3 and movingthe logical statements to the third row of the truth table. Antenna 1Ocontinues rotating in the reverse direction until the maximum signaldetector 12 senses a decrease in signal at B. This verifies that amaximum signal had been received and assures detection of a maximumsignal in instances where initial rotation of the antenna resulted in adecrease of signal strength (FIG. 10). Again the digital output ofvoltage comparator 13 changes to 0 and changes the logical statements tothe fourth row of the truth table. The antenna l0 reverses once more andgoes back to the apex C. When the binary counter 14 has counted twodecreases in signal strength, one on each side of a maximum signal, itlocates the maximum point of signal reception between these. When theincoming signal V, next reaches the amplitude shown at C, it changes thelogical statements to the fifth row of the truth table.

Upon reaching this state, shown at the fifth row of the truth table, theantenna 10 stops and M is at logical 1. This results in operation ofmemory eraser 17 to close switch 40 and erase the stored memory incapacitor 21. The output of the differential amplifier V becomesnegative and antenna 110 is latched at the position of maximum signalreception.

Remaining rows 6, 7 and 8 are unused logical statements in theillustrated circuits.

When the binary counter 14 is re-set manually by closing switch 40, theantenna may follow the above operation, shown as an ABCDCBC operation(FIG. 10). Alternately, initial reversal of the signal may result in adecline in signal strength, in which case the apparatus will follow aBABCDC operation as shown in FIG. 11. The description of the latter isessentially the same as that discussed with respect to FIGS. 9 and 10.

Various modifications might be made in the particular circuitry used tocarry out this invention. However, such modifications are believed to bewell within the skill of those knowledgable in the design of logiccircuits of the type discussed above.

Having thus described my invention, I claim:

1. In combination with a high frequency broadcast signal receivingantenna rotatably mounted on a support;

a reversible motor operatively connected between the support and antennafor selectively rotating the antenna so as to index the antenna forreception of a broadcast signal of maximum strength;

a motor control circuit operatively connected to the motor selectivelyoperable to cause the motor to rotate the antenna in oppositedirections;

and a receiver connected to the antenna;

the improvement in an automatic control for the motor control circuitcomprising:

memory means connected to the receiver for continuously monitoring thestrength of the instantaneous signal received thereby from the antenna,storing the maximum signal received and producing a comparative signalproportional to the difference in strength between the stored maximumsignal and the instantaneous signal received thereby;

comparator means operatively connected to said memory means forproducing a first digital output signal in response to reception of acomparative signal above a predetermined threshold level and a seconddigital output signal in response to reception of a comparative signalbelow the predetermined threshold level;

binary counter means operatively connected to said comparator means forcounting two reversals of the digital output signal from said comparatormeans for producing alternate control output signals dependent upon thenumber of digital output signals received thereby from said comparatormeans;

and logic switching means operatively connected to the binary countermeans and said motor control circuit for operating the motor inalternative directions of rotation in response to a predeterminedlogical sequence of control output signals to thereby reversibly rotatethe antenna to hunt and aim the antenna at an angular position at whichthe maximum signal strength of a selected station is received at saidreceiver.

2. The apparatus set out in claim 1, further comprising:

memory eraser means operatively connected to said memory means forerasing the maximum signal stored therein following aiming of theantenna at the angular position at which the maximum strength of aselected station is received and preventing production of a comparativesignal while the instantaneous signal received by the receiver remainsabove a predetermined reference level.

3. The apparatus set out in claim 2 wherein said logic switching meansis programmed to first initiate and continue rotation of the antennawhen the instantaneous signal received by the receiver falls below thepredetermined reference level, thereby deactivating said memory erasermeans.

4. The apparatus set out in claim 2 wherein said logic switching meansis programmed to first initiate and ative signal next falls below thepredetermined threshold level;

to then againreverse the direction of rotation when the comparativesignal again rises above the predetermined threshold level; and

finally to stop rotation of the antenna when the comparative signal nextfalls below the predetermined threshold level.

1. In combination with a high frequency broadcast signal receivingantenna rotatably mounted on a support; a reversible motor operativelyconnected between the support and antenna for selectively rotating theantenna so as to index the antenna for reception of a broadcast signalof maximum strength; a motor control circuit operatively connected tothe motor selectively operable to cause the motor to rotate the antennain opposite directions; and a receiver connected to the antenna; theimprovement in an automatic control for the motor control circuitcomprising: memory means connected to the receiver for continuouslymonitoring the strength of the instantaneous signal received therebyfrom the antenna, storing the maximum signal received and producing acomparative signal proportional to the difference in strength betweenthe stored maximum signal and the instantaneous signal received thereby;comparator means operatively connected to said memory means forproducing a first digital output signal in response to reception of acomparative signal above a predetermined threshold level and a seconddigital output signal in response to reception of a comparative signalbelow the predetermined threshold level; binary counter meansoperatively connected to said comparator means for counting tworeversals of the digital output signal from said comparator means forproducing alternate control output signals dependent upon the number ofdigital output signals received thereby from saiD comparator means; andlogic switching means operatively connected to the binary counter meansand said motor control circuit for operating the motor in alternativedirections of rotation in response to a predetermined logical sequenceof control output signals to thereby reversibly rotate the antenna tohunt and aim the antenna at an angular position at which the maximumsignal strength of a selected station is received at said receiver. 2.The apparatus set out in claim 1, further comprising: memory erasermeans operatively connected to said memory means for erasing the maximumsignal stored therein following aiming of the antenna at the angularposition at which the maximum strength of a selected station is receivedand preventing production of a comparative signal while theinstantaneous signal received by the receiver remains above apredetermined reference level.
 3. The apparatus set out in claim 2wherein said logic switching means is programmed to first initiate andcontinue rotation of the antenna when the instantaneous signal receivedby the receiver falls below the predetermined reference level, therebydeactivating said memory eraser means.
 4. The apparatus set out in claim2 wherein said logic switching means is programmed to first initiate andcontinue rotation of the antenna when the instantaneous signal receivedby the receiver falls below the predetermined reference level, therebydeactivating said memory eraser means; to next reverse the direction ofrotation of the antenna in response to reception of a comparative signalat the comparator means above the predetermined threshold level; tocontinue such reversed rotation when the comparative signal next fallsbelow the predetermined threshold level; to then again reverse thedirection of rotation when the comparative signal again rises above thepredetermined threshold level; and finally to stop rotation of theantenna when the comparative signal next falls below the predeterminedthreshold level.